Fit and comfort are arguably the two most important components of an article of footwear. This is especially true of any shoe type of footwear that includes some form of side or top restraint such as in a contoured sneaker or loafer. Improper fit can quickly lead to discomfort due to a tightly fitting shoe that pinches on the user's foot or a loosely fitting shoe that moves independently of the foot causing rubbing, irritation, and blisters. When shoes are made to a custom fit, these problems are rarely an issue. However, custom fitting presents a problem in today's economy where the cost of custom-made shoes is prohibitive. Moreover, one manufacturing trend is to produce generic, reusable components in order to reduce manufacturing costs, thus lowering the cost to the consumer.
These manufacturing constraints create significant limitations in the footwear industry. Each shoe size requires its own set of molds and therefore a capital investment on the part of the footwear company. Additionally, since different molds are created per shoe size, footwear companies need to spend time and effort to develop molds for each shoe size. Moreover, manufacturers tend to make sizes geared towards the mean or average dimensions of the population. This presents fit and comfort issues to users whose foot dimensions fall outside of the mean values. Furthermore, it is well known that there is a large range in foot dimensions within one shoe size.
To overcome these and other limitations, some companies produce shoes in different widths—smaller widths such as A and B, and wide widths, for instance E, EE or EEE. Although this helps some users with fit issues, it fails to satisfy many in the footwear wearing population and it presents significant complexity to the footwear company as they must offer, manufacture, stock, distribute, and account for more stock keeping units (“SKUs”). Also, it is well known that footwear companies accommodate for width adjustment by creating upper patterns with a larger girth and make no adjustments to other portions of the shoe, such as the outsole or the midsole. Therefore, it should be questioned how effective this manufacturing strategy is with supplying the most comfortable footwear. What is needed are improved shoes, as well as a method of manufacturing improved shoes that allows for the best fit and comfort for the user without creating additional complexity for the footwear manufacturer.
Anthropometric data of the foot determines the general shape and size of contemporary footwear. As discussed above, this data is used to develop shoes for the most likely consumer population and does not account for fit concerns of wearers outside of the statistical norm. In addition to the concerns of manufacturing to the mean of a population, there are a number of other issues that create fit and comfort issues.
By way of example only, there is a weak correlation between foot size versus height and weight. It is as likely to have a male with a weight of 145 pounds with a size 9 foot as it is to have a 225 pound male with a size 9 foot. This makes it difficult to adjust shoe and material specifications that would benefit comfort concerns for both males based solely on shoe size. For this reason, adjusting the density of the footbed to accommodate greater than normal loads should not be based solely on shoe size, but should also take into account the wearer's body mass and other factors.
Another issue is the fact that the shape and volume of the feet change under different conditions. Such conditions include the degree of weight bearing, the type of activity, and the climate. Feet tend to swell in hot and humid environments. The shape and volume of the foot also tends to change with age.
Yet another issue is the high incidence of mismatched feet (left/right) with regard to length, width, and girth of the feet. Left/right foot length differences of 15 mm (approximately 1.5 typical shoe sizes) are not uncommon. Approximately 30% of the population has foot lengths that have a difference of at least ½ shoe size, which is on the order of 5 mm.
In each of the above issues, adjusting shoe size due to the variability of the conditions cannot solve the problems. Therefore, it is desirable to solve the aforementioned problems in shoes that can be used by people with a wide spectrum of foot shapes and sizes, and allows the wearer to adjust shoe size to meet anatomical, physiological and environmental factors. It is also desirable to reduce the number of “Stock Keeping Units” (“SKUs”) offered in a product line, as this can generate substantial benefits throughout the supply chain.